Lysis is the disruption of the cell membrane, which is a standard process for not only eliminating pathogens but also accessing intracellular contents such as nucleic acids, proteins, metabolites, and other organelles. In particular, the extracted biomolecules from mammalian or microbial cells provide essential information about genetic or disease characteristics1. Thus, the cell lysis is the first procedure for various biological and clinical studies, including genomics, proteomics and metabolomics, with a wide range of applications in medicine and pharmacy, water-food-energy industry, agriculture, and for recovering of valuable intracellular products from recombinant cells.
Many conventional techniques have been developed to secure the highest yield and purity of the lysates from various organisms; among them, chemical, mechanical, and other physical methods were commonly employed. Chemical (detergents) or enzymatic permeation of the cell membrane was an attractive way of recovering lysates due to the simple operation and high lysis efficiency2-4, but the added reagents and proteins often hindered particular reactions and/or damaged lysates, resulting in narrow choices for downstream assays5. In addition, the chemical composition and concentration needed to be specifically optimized according to organisms so that it was difficult to be applicable for globally lysing various species in a complex cell mixture. By contrast, mechanical methods such as bead beating6, 7 and sonication8, 9, versatilely lysed any cell types without addictive ingredients10; however, they often require bulky and expensive equipment, and the lysis efficiency and recovery rate of lysates fluctuated greatly due to uncontrollable mechanical shearing of released intracellular biomolecules according to the apparatus and operational conditions8, 11. Moreover, it was often inefficient to apply the conventional mechanical lysis, which required somewhat large volume solutions to operate (>1 mL), using modern biochemical analysis tools (e.g., Nanostring) that only utilized a small quantity of samples (<50 μL) for executing genetic analysis12.
Electrical cell lysis would be a preferred method for microfluidic systems because the operational setting was simple without lytic additives and enabled prompt lysis using a sub-microliter solution with a wide range of cellular density (1-107 cells/mL)5, 13. Furthermore, the miniaturized electrical lysis module was directly integrated with post-processing elements, resulting in on-line, all-in-one, in-situ, and accurate analysis of the lysates14. However, for small cells such as bacteria (approximately 1 μm long and 0.5 μm thick), the required electric field was extremely high (>15 kV/cm)15 in order to satisfy the transmembrane potential for lysis (˜1.5 V)16, which might induce negative effects associated with high electric power, including biomolecule degradation, Joule heating, and water dissociation.
To alleviate the issues, the bacterial lysis by an electric field was only performed either in a low salinity solution (e.g., distilled water)17 for minimizing the current density or using a pinched microchannel (25 μm width)18 and small electrode gap (10-20 μm)19, 20 to reduce the electric potential. This eventually required additional steps to exchange buffers, and resulted in extremely low lysis throughput (<1 μL/min)18, 20-22. In this context, it was difficult for electrical lysis to produce enough quantity of lysates to implement off-chip post processing and analysis such as mass spectrometry or capillary electrophoresis, which generally required at least 100 μL solutions for handling. Recently, electrical cell permeation that also takes advantage of mechanical agitation (vortex) was reported to minimize the required electric field for permeating the membrane of mammalian cells23. However, challenges still exist in achieving reliable bacterial lysis that can be versatile and yet generally applicable to a wide range of bacterial pathogens, utilizing a low electric field and providing high throughput.